So it is unclear why Labour, whose front bench has shown greater willingness to recognise the value of the single market, should promulgate the idea that it is off limits under a Brexit deal.

Jeremy Corbyn said over the weekend that the single market and EU membership are “inextricably linked”. Barry Gardiner, shadow international trade secretary, goes further, envisaging Britain also outside the customs union – the outcome sought by the most zealous Tory Eurosceptics. Those are peculiar concessions for the opposition to be making now, especially since the vast majority of the party’s members (and millions of Labour voters) reject a hard Brexit.

The most commonly cited reason to accept the need to quit the single market is that staying in it entails adoption of free labour movement rules, thereby limiting options for border control.

Concern about immigration was a big driver of support for the leave campaign, so it is fair to fear a backlash against a Brexit deal that failed to reassure on that front. But free movement rules allow for stricter interpretation than has applied in Britain. And while the stated EU position is that porous borders are a non-negotiable part of the single market package, the potential for concessions and compromise is unknown, since it has not been probed.

Labour should be wary of complicity with Brexit arguments that are ultimately founded on the old Eurosceptic vilification of “open-door” policies that “flood” Britain with undesirable foreigners.